Normally low alloyed steels are used in waste incineration boilers. It is a well known problem that severe corrosion problems occur in such furnaces. It is a normal method primarily in the U.S.A. to protect such low alloyed material by overlay-welding a highly alloyed layer of a material such as A 625 which has been found to reduce the corrosion problems considerably. However, such overlay welding is not practically useful for tubes that are not used as panels such as super-heaters. An alternative to overlay-welding is the usage of composite tubes in which A 625 is used as an external layer. This should result in a good product from a corrosive aspect. However, such tubes are difficult to manufacture due to the large deformation forces that need to be used in hot working. The material is also sensitive to crack formation during cold working.
It is a complex challenge to provide a Ni-based alloyed material with good corrosion resistance and simultaneously good workability. However, by carrying out a systematic development work it has now been possible to provide a Ni-based alloy material that in a surprising manner can bring optimal properties in regard of corrosion resistance combined with hot workability, tensile strength and structure stability. By achieving these material properties, such material becomes useful not only as an external component in tubes for waste combustion furnaces but also as material used in black liquor recovery boilers, coal gasification, etc.